The present invention relates to a twin-cylinder circular knitting machine with a perfected device for actuating the transfer sinkers.
As is known, in twin-cylinder knitting machines it is necessary to operate in a different manner the transfer sinkers, or sliders, situated in the grooves of the lower needle-bearing cylinder which have transferred the corresponding needles into the upper needle-bearing cylinder, i.e. purl, with respect to the transfer sinkers which instead control the needles which operate in the lower cylinder, i.e. in plain knit.
During processing, in fact, the need arises to carry the point of the transfer sinkers, the needle of which is in the upper cylinder, to open the tab of the matching needle before the same reaches the feed from which it is to capture the thread, while the other transfer sinkers, which operate the plain-knit needles, must be operated so as to make the corresponding needle form knitting or to exclude the same from the forming of the knitting.
In order to achieve this diversified actuation, in the skirt of the cams of the lower cylinder two separate tracks are provided, with which engage respectively the heels of the transfer sinkers with plain-knit needles, or the heels of the transfer sinkers with purl needles; generally, the track with which the heels of the sinkers with purl needles engage, which can be eventually replaced by a track with which engage the heels of the selectors which act on these sinkers, is termed "memory".
The need to have two tracks in the skirt of the cams of the lower needle-bearing cylinder gives rise to some disadvantages, particularly in the case when it is desired to increase the rotation speed of the machine.
Indeed, due to the presence of a double path of the heels of the transfer sinkers, the slopes of the ascending and descending portions of the tracks, in which the heels of the transfer sinkers engage, have rather significant inclinations such as to prevent a satisfactory performance of the machine at high speeds without entailing rapid and damage of the sinkers.